多因子和多尺度合成中国夏季降水预测模型及预报试验

根据青藏高原60个站平均的月积雪深度、热带太平洋Ni^no 3区月海温和中国160个站月降水量等资料,用小波变换和相关分析,分析了1958~1998年秋冬季青藏高原异常雪盖与El Ni^no南方涛动(ENSO)的关系、多时间尺度变化的特征及其与中国夏季降水的相关型式。并取青藏高原积雪和Ni^no 3区海温的年际变化、年代际变化和线性趋势三种不同时间尺度的小波分量作为预报因子,对我国夏季降水距平作线性回归,建立了相应的预测模型。最后,利用1999~2002年的独立资料进行了预报试验,并在2003年和2004年应用于实际预报。研究表明,青藏高原雪盖与ENSO这两个物理因子彼此具有一定的独立性。它们都是多时间尺度现象,并与中国夏季降水有较好的关系。在不同时间尺度上不仅有不同的相关型式,而且相对贡献也有变化。回归预测模型的拟合情况和预报试验表明,综合考虑前期秋冬季青藏高原雪盖和ENSO这两个物理因子的年际变化、年代际变化和线性趋势作为预报因子建立的预测我国夏季降水距平分布的模型,有一定的预报能力。

基于BP神经网络的佛山空气质量预报模型的研究

提出非数值的佛山惠景城站点空气质量预报模型,将BP神经网络引入到预报模型中,以降雨量、风速、风向、温度、湿度和云量等气象参数和前1 d污染物浓度为模型输入参数,建立了结构为7-7-1的非季节预报模型和夏季预报模型。结果表明,夏季模型无论在模型检验还是在实际预报精度方面都略优于非季节模型。夏季模型的级别预报评分基本在90分以上,综合评分比非季节模型高10%。对夏季模型进行了参数敏感性分析,结果表明具有较好的稳定性。

An Experiment of a Statistical Downscaling Forecast Model for Summer Precipitation over China

A combination of the optimal subset regression (OSR) approach,the coupled general circulation model of the National Climate Center (NCC-CGCM) and precipitation observations from 160 stations over China is used to construct a statistical downscaling forecast model for precipitation in summer.Retroactive forecasts are performed to assess the skill of statistical downscaling during the period from 2003 to 2009.The results show a poor simulation for summer precipitation by the NCCCGCM for China,and the average spatial anomaly correlation coefficient (ACC) is 0.01 in the forecast period.The forecast skill can be improved by OSR statistical downscaling,and the OSR forecast performs better than the NCC-CGCM in most years except 2003.The spatial ACC is more than 0.2 in the years 2008 and 2009,which proves to be relatively skillful.Moreover,the statistical downscaling forecast performs relatively well for the main rain belt of the summer precipitation in some years,including 2005,2006,2008,and 2009.However,the forecast skill of statistical downscaling is restricted to some extent by the relatively low skill of the NCCCGCM.

The Coupled Model Predictability of the Western North Pacific Summer Monsoon with Different Leading Times

Leading time length is an important issue for modeling seasonal forecasts. In this study, a comparison of the interannual predictability of the Western North Pacific (WNP) summer monsoon between different leading months was performed by using one-, four-, and sevenmonth lead retrospective forecasts (hindcasts) of four coupled models from Ensembles-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) for the period of 1960 2005. It is found that the WNP summer anomalies, including lower-tropospheric circulation and precipitation anomalies, can be well predicted for all these leading months. The accuracy of the four-month lead prediction is only slightly weaker than that of the one-month lead prediction, although the skill decreases with the increase of leading months.

The Relationship between the East Asian Subtropical Westerly Jet and Summer Precipitation over East Asia as Simulated by the IAP AGCM4.0

Based on a 30-year Atmospheric Model Intercomparison Project(AMIP) simulation using IAP AGCM4.0, the relationship between the East Asian subtropical westerly jet(EASWJ) and summer precipitation over East Asia has been investigated, and compared with observation. It was found the meridional displacement of the EASWJ has a closer relationship with the precipitation over East Asia both from model simulation and observation, with an anomalous southward shift of EASWJ being conducive to rainfall over the Yangtze-Huaihe River Valley(YHRV), and an anomalous northward shift resulting in less rainfall over the YHRV. However, the simulated precipitation anomalies were found to be weaker than observed from the composite analysis, and this would be related to the weakly reproduced mid-upper-level convergence in the mid-high latitudes and ascending motion in the lower latitudes.

Numerical Study on Density Residual Currents of the Bohai Sea in Summer

M 2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. The tidal results showed good agreement with previous work. The model results indicated that the density residual currents are robust in summer; and that at the transition zone between well-mixed and stratified water, the horizontal velocity is high and the vertical velocity is positive.

The Extreme Summer Precipitation over East China during 1982-2007 Simulated by the LASG/IAP Regional Climate Model

The extreme summer precipitation over East China during 1982-2007 was simulated using the LASG/IAP regional climate model CREM(the Climate version of a Regional Eta-coordinate Model).The results show that the probability density functions(PDFs) of precipitation intensities are reasonably simulated,except that the PDFs of light and moderate rain are underestimated and that the PDFs of heavy rain are overestimated.The extreme precipitation amount(R95p) and the percent contribution of extreme precipitation to the total precipitation(R95pt) are also reasonably reproduced by the CREM.However,the R95p and R95pt over most of East China are generally overestimated,while the R95p along the coastal area of South China(SC) is underestimated.The bias of R95pt is consistent with the bias of precipitation intensity on wet days(SDII).The interannual variation for R95p anomalies(PC1) is well simulated,but that of R95pt anomalies(PC2) is poorly simulated.The skill of the model in simulating PC1(PC2) increases(decreases) from north to south.The bias of water vapor transport associated with the 95th percentile of summer daily precipitation(WVTr95) explains well the bias of the simulated extreme precipitation.

A Seasonal Prediction Model for the Summer Rainfall in Northeast China Using the Year-To-Year Increment Approach

Using the year-to-year increment approach,this study investigated the relationship of selected climatic elements with the increment time series of the summer rainfall between successive years in Northeast China,including the soil moisture content,sea surface temperature,500 hPa geopotential height,and sea level pressure in the preceding spring for the period 1981-2008.Two spring predictors were used to construct the seasonal prediction model:the area mean soil moisture content in Northwest Eurasia and the 500 hPa geopotential height over Northeast China.Both the cross-validation and comparison with previous studies showed that the above two predictors have good predicting ability for the summer rainfall in Northeast China.

Monsoon Change in East Asia in the 21st Century: Results of RegCM3

The authors investigate monsoon change in East Asia in the 21st century under the Special Report on Emissions Scenarios (SRES) A1B scenario using the results of a regional climate model, RegCM3, with a high horizontal resolution. First, the authors evaluate the model's performance compared with NCEP-NCAR reanalysis data, showing that the model can reliably reproduce the basic climatology of both winter and summer monsoons over East Asia. Next, it is found that the winter monsoon in East Asia would slightly weaken in the 21st century with spatial differences. Over northern East China, anomalous southerly winds would dominate in the mid-and late-21st century because the zonal land-sea thermal contrast is expected to become smaller, due to a stronger warming trend over land than over ocean. However, the intensity of the summer monsoon in East Asia shows a statistically significant upward trend over this century because the zonal land-sea thermal contrast between East Asia and the western North Pacific would become larger, which, in turn, would lead to larger sea level pressure gradients throughout East Asia and extending to the adjacent ocean.

How Large Precipitation Changes over Global Monsoon Regions by CMIP5 Models?

Future changes in precipitation over global monsoon domains and their adjacent dry regions are investigated using present-day climate simulations(1986–2005)and future climate simulations under the Representative Concentration Pathways(RCP4.5)scenario by the Coupled Model Intercomparison Project Phase 5(CMIP5)models.In the present-day climate simulations,high reproducibility of the extents of global monsoon domains and dry regions is observed from the multi-model ensemble(MME)result;the associated local summer precipitation variation and its interannual variability are also successfully reproduced.In the future,the global monsoon domains are projected to be expanded,while the dry regions are expected to initially increase and then decrease.The summer precipitation and its variability show significant increases over most global monsoon domains and obvious decreases over their adjacent dry regions.These results indicate that currently wet regions will become wetter and dry areas will be dryer under global warming conditions.Further analysis indicates that changes in summer precipitation over global monsoon and dry regions can be interpreted as moisture convergence changes associated with changes in horizontal moisture transport.

NUMERICAL SIMULATION EXPERIMENTS OF THE IMPACTS OF LOCAL LAND-SEA THERMODYNAMIC CONTRASTS ON THE SCS SUMMER MONSOON ONSET

The important effects of local land-sea thermodynamic contrast between the South China Sea (SCS) and Indochina Peninsula on SCS summer monsoon onset are preliminarily studied by using two sets of SSTA tests and two ideal tests in s-p regional climate model. The result shows that warm SST in the SCS in winter and spring is favorable for the formation of monsoon circulation throughout all levels of the atmosphere over the sea, which hastens the onset of SCS summer monsoon. The effects of cold SST are generally the opposite. The local land-sea contrast in the SCS is one of the possible reasons for SCS summer monsoon onset. Superposed upon large-scale land-sea thermodynamic differences, it facilitates the formation of out-breaking onset characteristics of SCS summer monsoon in the SCS area.

Statistical Downscaling of FGOALS-s2 Projected Precipitation in Eastern China

A statistical regression downscaling method was used to project future changes in precipitation over eastern China based on Phase 5 of the Coupled Model Intercomparison Project （CMIPS） the Representative Concentration Pathway （RCP） scenarios simulated by the second spectral version of the Flexible Global Ocean- Atmosphere-Land System （FGOALS-s2） model. Our val- idation results show that the downscaled time series agree well with the present observed precipitation in terms of both the annual mean and the seasonal cycle. The regres- sion models built from the historical data are then used to generate future projections. The results show that the en- hanced land-sea thermal contrast strengthens both the subtropical anticyclone over the western Pacific and the east Asian summer monsoon flow under both RCPs. However, the trend of precipitation in response to warming over the 21 st century are different across eastern Chi- na under different RCPs. The area to the north of 32°N is likely to experience an increase in annual mean precipitation, while for the area between 23°N and 32°N mean precipitation is projected to decrease slightly over this century under RCP8.5. The change difference between scenarios mainly exists in the middle and late century. The land-sea thermal contrast and the associated east Asian summer monsoon flow are stronger, such that precipitation increases more, at higher latitudes under RCP8.5 compared to under RCP4.5. For the region south of 32°N, rainfall is projected to increase slightly under RCP4.5 but decrease under RCP8.5 in the late century. At the high resolution of 5 km, our statistically downscaled results for projected precipitation can be used to force hydrological models to project hydrological processes, which will be of great benefit to regional water planning and management.

Global and Regional Impacts of Vegetation on the Hydrological Cycle and Energy Budget as Represented by the Community Atmosphere Model (CAM3)

The effects of vegetation and its seasonal variation on energy and the hydrological cycle were examined using a state-of-the-art Community Atmosphere Model （CAM3）. Three 15-year numerical experiments were completed： the first with realistic vegetation characteristics varying monthly （VEG run）, the second without vegetation over land （NOVEG run）, and the third with the vegetation characteristics held at their annual mean values （VEGMEAN run）. In these models, the hydrological cycle and land surface energy budget were widely affected by vegetation. Globaland annual-mean evapotranspiration significantly increased compared with the NOVEG by 11.8% in the VEG run run, while runoff decreased by 13.2% when the realistic vegetation is incorporated. Vegetation plays different roles in different regions. In tropical Asia, vegetation-induced cooling of the land surface plays a crucial role in decreasing tropical precipitation. In middle latitudes and the Amazon region, however, the vegetation-induced increase of evapotranspiration plays a more important role in increasing precipitation. The seasonal variation of vegetation also shows clear influences on the hydrological cycle and energy budget. In the boreal mid-high latitudes where vegetation shows a strong seasonal cycle, evapotranspiration and precipitation are higher in the summer in the VEG run than in the VEGMEAN run.

Statistically Downscaled Summer Rainfall over the Middle-Lower Reaches of the Yangtze River

The summer rainfall over the middle-lower reaches of the Yangtze River valley (YRSR) has been estimated with a multi-linear regression model using principal atmospheric modes derived from a 500 hPa geopotential height and a 700 hPa zonal vapor flux over the domain of East Asia and the West Pacific.The model was developed using data from 1958 92 and validated with an independent prediction from 1993 2008.The independent prediction was efficient in predicting the YRSR with a correlation coefficient of 0.72 and a relative root mean square error of 18%.The downscaling model was applied to two general circulation models (GCMs) of Flexible Global Ocean-Atmosphere-Land System Model (FGOALS) and Geophysical Fluid Dynamics Laboratory coupled climate model version 2.1 (GFDL-CM2.1) to project rainfall for present and future climate under B1 and A1B emission scenarios.The downscaled results pro-vided a closer representation of the observation compared to the raw models in the present climate.In addition,compared to the inconsistent prediction directly from dif-ferent GCMs,the downscaled results provided a consistent projection for this half-century,which indicated a clear increase in the YRSR.Under the B1 emission scenario,the rainfall could increase by an average of 11.9% until 2011 25 and 17.2% until 2036 50 from the current state;under the A1B emission scenario,rainfall could increase by an average of 15.5% until 2011 25 and 25.3% until 2036 50 from the current state.Moreover,the increased rate was faster in the following decade (2011 25) than the latter of this half-century (2036 50) under both emissions.

Hydrological Impacts of Climate Change on Streamflow of Dongliao River Watershed in Jilin Province,China

The impacts of future climate change on streamflow of the Dongliao River Watershed located in Jilin Prov-ince, China have been evaluated quantitatively by using a general circulation model （HadCM3） coupled with the Soil and Water Assessment Tool （SWAT） hydrological model. The model was calibrated and validated against the historical monitored data from 2005 to 2009. The streamflow was estimated by downscaling HadCM3 outputs to the daily mean temperature and precipitation series, derived for three 30-year time slices, 2020s, 2050s and 2080s. Results suggest that daily mean temperature increases with a changing rate of 0.435~C per decade, and precipitation decreases with a changing rate of 0.761 mm per decade. Compared with other seasons, the precipitation in summer shows significant downward trend, while a significant upward trend in autumn. The annual streamflow demonstrates a general down-ward trend with a decreasing rate of 0.405 m^3/s per decade. The streamflow shows significant downward and upward trends in summer and in autumn, respectively. The decreasing rate of streamflow in summer reaches 1.97 m^3/s per decade, which contributes primarily to the decrease of streamflow. The results of this work would be of great benifit to the design of economic and social development planning in the study area.

Inter-decadal Variability of the East Asian Summer Monsoon and Its Impact on Hydrologic Variables in the Haihe River Basin, China

Wavelet analysis and Mann-Kendall tests are employed to evaluate the variation in the East Asian summer monsoon（EASM） and hydrological variables in the Haihe River basin calculated by the Variable Infiltration Capacity model. The relationships between those variables and the EASM are also examined. The results indicate consistent 40 a periodic variation in both the hydrological variables and the EASM. The hydrologic variables show downward trends in the Haihe River basin over the past 60 years, especially in piedmont regions of the Taihang-Yan Mountains. The variables are closely related to the EASM, whose continuous weakening since the 1970 s has resulted in prolonged drought and severe water shortages in the basin. The periodicity of the EASM index was analyzed using continuous wavelet transform methods. We found the most significant periodic signal of the EASM is ~80 years; therefore, the EASM may reinforce and reach a maximum in the 2040 s, resulting in more precipitation and other impacts on basin water resources. Hydrologic variables in the basin in the 2040 s are predicted, and their spatial distributions in the Haihe River basin are also discussed. These results allow for the estimation of water resources under forecasted EASM, which will be useful for water resources management in the Haihe River basin.

Reconstruction of Conceptual Prediction Model for the Three Rainfall Patterns in the summer of eastern China under global warming

With the influence of global warming,the global climate has undergone significant inter-decadal variation since the late 1970s.Although El Nio-Southern Oscillation(ENSO)has been the strongest signal for predicting global climate inter-annual variability,its relation with the summer rainfall in China has significantly changed,and its indicative function on the summer rainfall in China has weakened.This has led to a significant decrease in the accuracy rate of early conceptual prediction models for the Three Rainfall Patterns in the summer of eastern China.On the basis of the difference analysis of atmospheric circulation system configuration in summer,as well as the interaction of ocean and atmospheric in previous winter between two phases,i.e.before and after the significant global warming(1951 to 1978 and 1979 to 2012,respectively),we concluded that(1)Under different inter-decadal backgrounds,the atmospheric circulations that impacted the Three Rainfall Patterns in the summer of eastern China showed consistency,but in the latter phase of the global warming,the Western Pacific Subtropical High(WPSH)was on the strong side,the position of which was in the south,and the blocking high in the Eurasia mid-high latitudes was active,while the polar vortex extended to the south,and meridional circulation intensified.This circulation background may have been conducive to the increase of the circulation frequency of Patterns II and III,and the decrease of the circulation frequency of Pattern I,thus leading to more Patterns II and III and fewer Pattern I in the summer rainfall of eastern China.(2)In the former phase,the corresponding previous winter SST fields of different rainfall patterns showed visible differences.The impact of ENSO on North Pacific Oscillation(NPO)was great,and the identification ability of which on Patterns I and II of summer rainfall was effective.In the latter phase,this identification ability decreased,while the impact of ENSO on the Pacific/North American(PNA)teleconnection pattern increased,and the identification ability of the PNA on Patterns II and III also increased.Based on the new inter-decadal climate background,this study reconstructs the conceptual prediction model for the Three Rainfall Patterns in summer of eastern China by using the previous winter PNA and the Eurasian(EU)teleconnection indexes.The fitting effect was satisfying,though it is necessary to be further tested.

The projected temporal evolution in the interannual variability of East Asian summer rainfall by CMIP3 coupled models

The projected temporal evolution in the interannual variability of East Asian summer rainfall in the 21st century is investigated here,by analyzing the simulated results of 18 coupled models under the 20th century climate experiment and scenario A1B.The multi-model ensemble(MME)mean projects two prominent changes in the interannual variability of East Asian summer rainfall in the 21st century under scenario A1B.The first change occurs around the 2030s,with a small change before and a large increase afterward.The intensity of the interannual variability increases up to approximately 0.53 mm/d in the 2070s,representing an increase of approximately 30% relative to the early 21st century.The second change happens around the 2070s,with a decrease afterward.By the end of the 21st century,the increase is approximately 12% relative to the early 21st century.The interannual variability of two circulation factors,the western North Pacific subtropical high(WNPSH)and the East Asian upper-tropospheric jet(EAJ),are also projected to exhibit two prominent changes around the 2030s and 2070 under scenario A1B,with consistent increases and decreases afterward,respectively.The MME result also projects two prominent changes in the interannual variability of water vapor transported to East Asia at 850 hPa,which occurs separately around the 2040s and 2070s,with a persistent increase and decrease afterward.Meanwhile,the precipitable water interannual variability over East Asia and the western North Pacific is projected to exhibit two prominent enhancements around the 2030s and 2060s and an increase from 0.1 kg/m2 in the early 21st century to 0.5 kg/m2 at the end of the 21st century,implying a continuous intensification in the interannual variability of the potential precipitation.Otherwise,the intensities of the three factors'(except EAJ)interannual variability are all projected to be stronger at the end of the 21st century than that in the early period.These studies indicate that the change of interannual variability of the East Asian summer rainfall is caused by the variability of both the dynamic and thermodynamic variables under scenario A1B.In the early and middle 21st century,both factors lead to an intensified interannual variability of rainfall,whereas the dynamic factors weaken the interannual variability,and the thermodynamic factor intensifies the interannual variability in the late period.

Large shear rate behavior for the Hebraud-Lequeux model Dedicated to the NSFC-CNRS Chinese-French summer institute on fluid mechanics in 2010

The H@braud-Lequeux model is a model describing the flow of soft glassy material in a simple shear flow configuration. It is given by a kinetic/Fokker-Planck-type equation whose coefficients depend on the shear rate of the experiment. In this paper we want to study what happens to the stationary solutions of this model when the shear rate is asymptotically large. In order to do that, we expand the solution of the equation using singular perturbation tools. In the end, we rigorously prove the estimate of Hebraud and Lequeux that the material asymptotically behaves as a Newtonian fluid.